The present invention relates to systems that support a patient on a support surface defined by granular material that has been fluidized with pressurized air passing through the granular material and more particularly to such systems having improved control over the temperature of the patient support surface.
Typically, the air used to fluidize the granular material of a fluidized patient support system such as shown in U.S. Pat. No. 4,564,965 (which is hereby incorporated herein by this reference), is pressurized by an air blower. When the ambient air has passed through the blower, the temperature of the air has been increased by about 20.degree. C. or more. As this air impinges upon the patient supported on the fluidized support surface, the temperature of this air becomes a concern for patient care and comfort.
In U.S. Pat. No. 4,637,083, which is hereby incorporated herein by this reference, a fluidized patient support apparatus deploys a heat exchanger 54 between the fluid pressure generator means 50 and a common fluid pressure manifold 29, which carries the air that fluidizes the granular material 40 carried in the tank 15.
In U.S. Pat. No. 5,016,304which is hereby incorporated herein by this reference, an air drying unit 8 is interposed in the path of the air between the blower and the plenum chamber beneath the beads of a fluidized bed. Cooling of the fluidizing air takes place in the air treatment chamber 8, and this condenses moisture from the air in chamber 8 such that dry air arrives in the fluidization chamber 2 via a duct 4 and the distribution space 3 and can return to the surrounding atmosphere via the lying surface 1a. The evaporating means 7 located in air treatment chamber 8, is part of a cooling circuit which consists of a compressor 12 and a condenser 13. Compressor 12 regulates transportation of a coolant such as freon via the connecting lines in the direction of arrow P.sub.2 along the previously mentioned evaporating means 7. However, the use of freon gas in the hospital environment is to be avoided in general and in particular in a fluidized bed so that an accidental leakage of freon cannot become mixed with fluidization air.
In U.S. Pat. No. 4,609,854, which is hereby incorporated herein by this reference, a fluidized bed is provided with a cooler 7 to cool air that is supplied to a tank 2 containing the beads of a fluidized bed. A sensor S1 is provided in tank 2 to detect the temperature of the beads. A fan motor FM circulates air around the cooling fins of cooler 7 so that cooled, compressed air causes the beads to move around in tank 2.
In U.S. Pat. No. 4,723,328, which is hereby incorporated herein by this reference, a fluidized bed includes a radiator 11 in a conduit 10, which couples an air blower to the plenum chamber so that the blower can supply compressed air to the plenum chamber.